1. Field of the Invention
The present invention relates to a method of fabricating a semiconductor device and, more particularly, to a method of fabricating a semiconductor device by which a substrate may be prevented from being bent, and a semiconductor device fabricated by the same method.
2. Description of Related Art
Polycrystalline silicon is used in an active device for an organic light emitting display device, normally, thin film transistors (TFTs), which is used to supply current to pixel regions and peripheral driving regions.
In general, the polycrystalline silicon is formed by crystallization of amorphous silicon.
Normally, methods for the crystallization may be largely classified into a low-temperature crystallization method and a high-temperature crystallization method depending on a crystallization temperature, for example, with reference to about 500° C.
An excimer laser annealing (ELA) method using an excimer laser is mainly used as the low-temperature crystallization method. The eximer laser annealing method may use a glass substrate since it is carried out at a crystallization temperature of about 450° C. However, manufacturing cost is high and the substrate is constrained in an optimal size, thereby increasing total cost to fabricate a display device.
The high-temperature crystallization method includes a solid phase crystallization method, a rapid thermal annealing method, and the like. A low-cost annealing method is widely used as the high-temperature crystallization method.
However, since the solid phase crystallization method requires heating at a temperature of more than 600° C. for 20 or more hours for crystallization, many crystal defects are included in the crystallized polycrystalline silicon. Accordingly, sufficient electric field mobility cannot be obtained, the substrate is prone to deform during an annealing process, i.e., a heat treatment process, and lowered crystallization temperature degrades productivity. Because the solid phase crystallization method is also performed at high crystallization temperature, a glass substrate may be used.
Meanwhile, although the rapid thermal annealing (RTA) method may be accomplished in relatively short time, the substrate is prone to deform due to severe thermal shock and the crystallized polycrystalline silicon has poor electrical characteristics.
Consequently, a low-cost high-temperature annealing method may be required to be used upon the crystallization in order to reduce cost to fabricate the active device. Moreover, there is a need for a high-temperature annealing method using an inexpensive glass substrate, by which the glass substrate is not bent and crystallinity is excellent.